The term "vegetables" as used herein is intended to include tubers and root vegetables especially potatoes, carrots, turnips, salsify and even asparagus. Since the potato is the dominant vegetable of this class with respect to its share of the market, the invention will be described primarily in connection therewith, although reference in the body of the description to the potato is not to be considered a limitation to it, but rather the identification of a vegetable of the class with which the invention is operative and hence by way of example rather than by way of limitation.
Reference will also be made herein to the presentation of a vegetable product for marketing. It is intended to thus identify a product which is packaged, has a comparatively long shelf life, and has a pleasing appearance, i.e. an appearance which is attractive to the point that a potential customer may be induced to purchase the product and to try it. Of course this preparation for marketing also includes the presentation of the product in a form which facilitates its use by the consumer.
Traditionally potatoes have been marketed in a raw state, in a condition of limited shelf life or duration to spoilage. After purchase, the potatoes must be peeled before they can be used.
To overcome both drawbacks, it has been proposed to treat potatoes in various ways to increase their storage life and facilitate their use. For example, the potatoes can be precooked after having been peeled, washed and "bleached" to prevent or limit discoloration during processing. The precooked product has a storage life of several days when maintained under refrigeration at temperatures of +2.degree. to +5.degree. C.
To open other potential markets for potatoes, they have been subjected to processes allowing them to be utilized in so called "instant" form, e.g. simply by the addition of water.
It has also been proposed to put up potatoes in a form which facilitates preparing a dish therefrom by a process involving a deep sterilization of the potato after it has been peeled and washed. In this case, the potatoes may be placed in pouches of synthetic resin material which are conditioned in vacuo and sterilized.
Potatoes treated in this way do indeed have a relatively long shelf life, but their commercial exploitation has been sharply inhibited by their high price. This is due to two key factors. Firstly, it is necessary to treat the material in a highly dense state and thus to work at a temperature between 115.degree. and 125.degree. C., thereby requiring considerable energy. Consequently, the conditioning of the potatoes in the pouches is a problem because they have a consistency which makes them difficult to subject to such temperatures.
In spite of their high cost, however, potatoes sterilized in this fashion do not have any culinary advantages and indeed present culinary disadvantages because they develop a sticky consistency and appearance, are sensitive to shock and, because they are entirely cooked by the sterilization at the elevated temperatures, it is not possible to prepare them in certain forms, for example, cut up cold in a vinaigrette sauce or to fry them in a pan.
In many cases, fully sterilized potatoes of the type described have more drawbacks than advantages.
It has been proposed in French applicatiion No. 79 23 860 to overcome some of these drawbacks by a succession of treatments including a pasteurization to obtain potatoes whose storage life may be less than that of sterilized potatoes, but which are produced in a form which permits their use in the same manner as raw potatoes.
Thus the problem of preserving tuber and root vegetables of the types described and especially potatoes so that they can be stored for reasonably long periods without refrigeration, e.g. at room temperature, has long been a perplexing one.